Most healthy people open their bowels between three times a day and three times a week. Normal stools are usually solid. The term diarrhoea is used when stools are passed more than three times a day and when the stools become loose or watery. In acute diarrhoea, symptoms come on suddenly but usually clear up within 5-10 days. 

What are the mechanisms of acute diarrhoea?

• Normal stools are solid because the small intestine and colon are highly efficient in absorbing nutrients, fluid and salts from the liquid, upper gut contents.

•  Diarrhoea occurs when these processes are impaired, for example when the lining of the gut is damaged by bacteria or viruses.

•  Diarrhoea can also occur when there is excessive secretion of fluid into the bowel that overwhelms the ability of the gut to reabsorb the secreted fluid and salts. Some laxative drugs have this effect although the most common cause relates to infection with bacteria that produce proteins (enterotoxins) that stimulate gut secretion. In some situations acute diarrhoea may occur as a result of a combination of both mechanisms.

•  Diarrhoea may result when the bowel contents move too rapidly through the gut to allow sufficient time for absorption. Anxiety and some drugs can cause diarrhoea in this way. Bowel frequency is sometimes increased in people with irritable bowel syndrome. However, there is no increase in stool volume which distinguishes it from acute diarrhoea, when stool volume is increased.

What are the causes of acute diarrhoea?

• The most common cause of an attack of acute diarrhoea is an intestinal infection ('gastroenteritis'). Infants and young children are particularly susceptible to intestinal infections which are most commonly caused by a rotavirus.
• Food poisoning is another common form of acute diarrhoea, most commonly caused by the bacteria Salmonella and Campylobacter. These infections are passed on through contaminated food, such as poultry and eggs, or water; and sometimes by a person such as food handler who has the infection, but has no symptoms of that infection (a carrier).
• People who travel a lot are also susceptible to intestinal infection, the most common cause being the bacterium, Escherichia coli. This organism releases enterotoxins in the gut, which produce intestinal secretion.
• Acute diarrhoea can sometimes occur during or after a course of antibiotics, as a result of a variety of drugs and alcohol, and is associated with attacks of acute anxiety.

What are the symptoms that might be associated with acute diarrhoea?

Acute intestinal infections are commonly associated with cramping central or lower abdominal pain. Some infections may cause fever, particularly infections due to Shigella and Campylobacter that get into the lining of the bowel and cause acute inflammation. When there is direct damage to the bowel, blood may be associated with the diarrhoea (dysentery).